give readdir(2)/getdents(2)/etc. uniform exclusion with lseek()

same as read() on regular files has, and for the same reason.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/include/linux/file.h b/include/linux/file.h
index f87d308..7444f5f 100644
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -44,6 +44,7 @@
 extern unsigned long __fdget(unsigned int fd);
 extern unsigned long __fdget_raw(unsigned int fd);
 extern unsigned long __fdget_pos(unsigned int fd);
+extern void __f_unlock_pos(struct file *);
 
 static inline struct fd __to_fd(unsigned long v)
 {
@@ -60,6 +61,18 @@
 	return __to_fd(__fdget_raw(fd));
 }
 
+static inline struct fd fdget_pos(int fd)
+{
+	return __to_fd(__fdget_pos(fd));
+}
+
+static inline void fdput_pos(struct fd f)
+{
+	if (f.flags & FDPUT_POS_UNLOCK)
+		__f_unlock_pos(f.file);
+	fdput(f);
+}
+
 extern int f_dupfd(unsigned int from, struct file *file, unsigned flags);
 extern int replace_fd(unsigned fd, struct file *file, unsigned flags);
 extern void set_close_on_exec(unsigned int fd, int flag);